Effects of cAMP, cGMP, and several agents promoting their accumulation on 3H-thymidine and 14C-leucine incorporation and cyclic nucleotide levels in corneal epithelial cell cultures were examined. 8-bromo-cGMP significantly enhanced thymidine and leucine incorporation (p less than 0.05), as did acetylcholine and carbamylcholine, which elevated cGMP and decreased cAMP/cGMP ratio. Both atropine sulfate and alpha-bungarotoxin blocked the responses to acetylcholine. Precursor incorporation was inhibited by dibutyryl cAMP, adenosine 5'-monophosphate, and theophylline, which significantly elevated cAMP levels. Norepinephrine and epinephrine significantly elevated cAMP and cAMP/cGMP ratio and depressed thymidine and leucine incorporation. Propranolol, but not phenoxybenzamine, blocked these responses to effective concentrations of norephinephrine, supporting the operation of a beta-adrenergic mechanism. Prostaglandins E1 and F2-alpha were very potent in increasing cAMP levels and cAMP/cGMP ratio, although both at certain concentrations also elevated cGMP. Both prostaglandins were highly effective inhibitors of precursor incorporation over a wide range of concentrations. Results were consistent with a cGMP-mediated role of the cholinergic transmitter in corneal epithelial growth regulation, cAMP-mediated adrenergic suppression of regrowth after initial wounding of corneal epithelium, and potentiation of the adrenergic effect by prostaglandins or other inflammatory substances.